The invention relates to an improved seal for an air cushion vehicle.
The U.S. Navy has undertaken a considerable amount of research on the surface effect ship (SES) which is characterized by its hard catamaran like side hulls with bow and stern seals. With this arrangement, an air cushion is obtainable between the side hulls and the seals for positioning the vehicle above the surface of the water.
There have been various designs of bow and stern seals ranging from fully flexible seals to partially rigid seals. Various embodiments of bow and stern seals are illustrated in the following patents: U.S. Pat. No. 4,137,987 to Plackett; U.S. Pat. No. 4,215,756 to Hunt; U.S. Pat. No. 4,285,414 to Malakhoff et al; U.S. Pat. No. 3,410,241 to Hardy et al; U.S. Pat No. 3,424,266 to Cockerell; and U.S. Pat. No. 4,000,710 to Crago. The purposes of a bow or stern seal are: (1) to minimize leakage from the pressurized air cushion region to the atmosphere and thereby minimize cushion air flow power requirements; (2) absorb wave impacts and thereby reduce structural loads; and (3) provide restoring forces to maintain pitch stability.
In order to prevent excessive leakage of cushion air to the atmosphere it is necessary that a bow or stern seal follow the high frequency smaller wave surfaces as well as the larger wave surfaces. This requires that the lower end of the seal be made of some highly flexible material. However, because of the highly dynamic environment at the lower end of the seal the flexible material rapidly wears so that replacement becomes a large factor in the operational cost and durability of the surface effect vehicle. There is a need for a flexible seal which is configured to minimize wear due to wave action, and yet be able to minimize drag during operation of the surface effect vehicle.